For quite a while now, the GCJ project has been adding Java support to GCC. It isn't perfect and building your big, using every API Java app with it could be a real pain. But it is getting better. Anyway, this is about working together.

Java has always had JNI for interfacing with other languages (generally C/C++). It works, but it's not exactly clean. GCJ, however, has the CNI which works much more nicely. A small example: